Python Conway's Game of Life

gistfile1.py

#!/usr/bin/env python

# Author: Michael-Keith Bernard
# Date: July 27, 2012
#
# Game of Life
#
# Ported from this clojure implementation:
#
# (defn neighbours [[x y]]
#   (for [dx [-1 0 1] dy (if (zero? dx) [-1 1] [-1 0 1])]
#     [(+ dx x) (+ dy y)]))
#
# (defn step [cells]
#   (set (for [[loc n] (frequencies (mapcat neighbours cells))
#              :when (or (= n 3) (and (= n 2) (cells loc)))]
#          loc)))
#
# Notes: See this Lua port of the same implementation:
#          https://gist.github.com/3186788
#
#        This code is almost definitely not idiomatic Python as such, but was
#        written to demonstrate the benefits of hashable and comparable types
#        over the relatively simplistic tables provided by Lua.

from os import system
from time import sleep
from random import randint
from collections import defaultdict

def concat(l):
  return [e for m in l for e in m]

def mapcat(f, l):
  return concat(map(f, l))

def freq(l):
  freqs = defaultdict(lambda: 0)
  for e in l:
    freqs[e] += 1
  return freqs

# Game of Life

def neighbors(point):
  x, y = point
  return [(x+dx, y+dy) for dx in range(-1,2) for dy in range(-1,2)
    if not (dx==0 and dy==0)]

def step(cells):
  new_cells = set()
  for (loc, cnt) in freq(mapcat(neighbors, cells)).items():
    if cnt == 3 or (cnt == 2 and loc in cells):
      new_cells.add(loc)
  return new_cells

def prune(cells, w, h):
  new_cells = set()
  for (x, y) in cells:
    if (x >= 0 and x <= w) and (y >= 0 and y <= h):
      new_cells.add((x,y))
  return new_cells

def new_board(w, h, fill=True):
  board = set()
  if fill:
    while len(board) < (w * h) / 4:
      board.add((randint(0,w), randint(0,h)))
  return board

def clear():
  system("clear")

def render(board, w, h):
  clear()
  for y in range(h):
    for x in range(w):
      if (x,y) in board:
        print "#",
      else:
        print ".",
    print
  print

def conway(w, h):
  board = new_board(w, h)
  gen = 0
  while True:
    if gen > 50 and randint(1, 100) > 95:
      board = new_board(w, h)
      gen = 0
    gen += 1
    render(board, w, h)
    board = prune(step(board), w, h)
    sleep(0.125)

conway(20, 20)